This invention relates to a medical device for the noninvasive location and imaging of peripheral nerves. Specifically, the present invention is a sensor system for use at the skin surface comprising an electrode array assembly with multiple electrodes and a skin attachment system. Each electrode in the electrode array assembly maintains a connection to peripheral nerve detection and imaging instrumentation. A negative return wire is attached to the electrode array assembly and to a skin surface electrode during use of the sensor system. A disposable, sterile skin attachment system allows conductance between the electrode array and the skin surface of the subject. The skin attachment system contains individual hydrogel islands, each adapted to align accurately with a specific electrode of the electrode array. The layer of the skin attachment system that adheres to the skin surface of the subject may be left on the skin at the end of sampling to provide a skin marking guide. This facilitates the positioning of needles for subsequent nerve stimulation or therapy.
The use of direct current skin surface conductance or resistance measurements has been employed in many forms for the identification of peripheral nerves, myofascial trigger points, and acupuncture points (Cory, et al., 1996; Kaslow and Lowenschuss, 1975; Kejariwal, et al., 1996; Kwok, et al., 1998; Lykken, 1971). An early example of this was the use of a transcutaneous electrical nerve stimulation (TENS) unit to identify acupuncture points. When a TENS unit is coupled between examiner and subject, the finger of the examiner acts as a sampling electrode (Kaslow and Lowenschuss, 1975). However, the literature in the field illustrates inconsistency in locating peripheral nervous tissue through electrical conductance measurements (Reichmanis et al., 1975).
U.S. Pat. No. 4,016,870 to Lock describes a system for acupuncture point location in which a single, hand-held probe of undisclosed composition is used to determine sites of high skin surface conductance. U.S. Pat. No. 5,897,505 to Feinberg, et al., describes a system for measuring selective tissue conductance and temperature utilizing chrome-plated, brass electrodes in a handheld embodiment. Although each of these systems measures conductance at the skin surface, they suffer two main drawbacks. First, metallic electrodes display uneven current densities at the skin surface-electrode interface, largely dependent on the underlying moisture pattern of the skin. Means for measuring skin surface conductance and resistance that do not employ aqueous interfaces are particularly subject to this effect (Cory, 1996; Freedman L W, 1994), and, in some cases, current densities became high enough to produce painful sensation. Second, handheld devices are subject to uncontrolled application pressures. This is complicated in larger diameter electrode systems, such as that of Feinberg, where the angle of application causes pressure to be unequally distributed on the skin surface. The use of electrical conductance measurements at the skin surface to locate nerve tissue is facilitated by the use of aqueous electrodes, rather than metallic or dry silver-silver chloride electrodes, and by the use of pulsed direct current as the device output, rather than alternating current (Kejariwal et al., 1996). Based upon observations such as these, a device that locates peripheral nerves transcutaneously was disclosed in U.S. Pat. No. 5,560,372 to Cory (the disclosure of which is incorporated herein by reference.)
The problem of avoiding metallic interfaces with the skin surface is addressed by the use of water-saturated felt electrodes in U.S. Pat. No. 5,560,372 to Cory and by the use of hydrogels (Jossinet and McAdams, 1990). The ability to obtain reproducible skin surface conductance and resistance readings allows the recognition of skin surface sites that correspond to underlying peripheral nerves (Cory, et al., 1996). While this approach circumvents the problems of current density disparities, of the formation of thin oxidation films on the electrodes, and of subsequent back electromotive force, additional problems remain that are associated with the interface between the sampling electrodes and the skin surface.
It is an object of the present invention to provide a sensor system comprising an electrode array and a skin attachment system for use with an electrical field generating device that can non-invasively detect peripheral nerves.
It is further an object of the present invention to provide a method for detecting peripheral nerves using the aforementioned sensor system.
It is further an object of the present invention to provide for an electrode array, which is flexible, reusable, and suitable for use in combination with a skin attachment system as herein described.
It is further an object of the present invention to provide for a skin attachment system, comprising hydrogel islands, which is disposable and suitable for use in combination with an electrode array as herein described.
Further objects and advantages of the invention will be apparent from the following description of the invention.